The present invention relates to a process for obtaining cold water extractable tea leaf and to the improved products thereby obtained. In particular, the invention relates to a method of treating fresh green tea leaf with the enzyme tannase to produce dry tea leaf, green, black or oolong, which is cold water extractable, and which has a full complement of the tea flavor associated with the corresponding prior art processes.
Black tea is usually prepared by subjecting freshly picked tea leaves to a series of processing conditions including the withering and rolling of freshly harvested leaves, followed by a fermentation step (enzymatic oxidation) during which much of the characteristic color, flavor and aroma of black tea are developed. The fermentation is stopped after a suitable period of time by "firing" (drying at temperatures ranging from about 65.degree. C to about 100.degree. C) the tea to inactivate the enzymes causing the fermentation and to complete the development of the flavor and color of the tea product. The extent of fermentation varies, in commercial practice, from black to various gradations between green and black. Partially fermented teas are known as "oolong" teas. Green teas are made by firing green tea before fermentation has taken place. The green, oolong, and black teas of commerce each provide a beverage having distinctive flavor and color characteristics.
When conventional teas are extracted with cold water for short periods of time (less than 15 minutes), the tea beverage produced has a low concentration of extractable tea solids, a very light color and almost no tea-like taste. Water at temperatures of about 100.degree. C is usually employed to obtain a satisfactory beverage with prior art tea leaves.
Various procedures are known to the art for making cold water soluble instant tea powders by solubilizing tea cream obtained from black tea extracts, e.g., Herz, U.S. Pat. No. 2,831,772; Perech, U.S. pat. No. 2,863,775; and Barch, U.S. Pat. No. 3,136,539. While each of these processes are successful to varying degrees in producing a cold water soluble instant tea powder, each has disadvantages. Most fail to provide a tea powder which, on reconstitution, gives a beverage having a natural flavor and color. Furthermore, none of these prior art processes provide a tea powder which will provide the "milk reaction" provided by natural tea. Naturally brewed tea, when milk is added, takes on a bright pinkish-reddish color which is pleasing to the eye. The instant tea powders produced by the prior art techniques described above, when reconstituted as a hot beverage, react badly to the addition of milk, taking on a dull unpleasant coloration.
One method utilizing tannase enzymes to produce cold water soluble instant tea powder is the subject of a copending application of Graham, Ser. No. 173,323, filed Aug. 19, 1971, now abandoned. It is also known from the Sanderson et al. U.S. Pat. No. b 3,812,266, that fresh green tea homogenate, when given a pre-conversion tannase treatment, will yield an instant tea powder which is cold water soluble.